The invention relates to a milling tool for machining wood, wooden materials, plastics or the like with at least one cutting edge arranged in the milling tool and a chip space or gap located in front of the cutting edge for chip collection and has an axial ejection opening for chip disposal which runs approximately perpendicular to a plane formed by the cutting edge and cutting direction and has a cross-section bigger than the projected area of a chip cut off during the cutting action of the cutting edge.
From DE 30 43 146 A1, a milling tool is known which has cutting edges arranged on a perimeter of the tool. During generation of cut-off chips, the chips are pushed into chip spaces located in front of the cutting edges where they remain until an end of each single cutting-off process is reached. As soon as the cutting edge leaves a workpiece surface the chips are transported due to the centrifugal force out of the chip spaces and then have to be removed from a work area and its environment by means of an accompanying exhaust system.
It is a disadvantage of this milling tool that the chips discharged possess a high level of kinetic energy and have to be caught and transported away using complicated chip hoods and high suction air rates, which produces high costs. With increasing cutting speed and rate of revolutions, the exhaust speed and air rate required to collect and transport away the chips and to observe regulations on the residual dust content of the air also increase.
Not all generated chips are collected by the exhaust system and can accumulate at the workpiece surface. This can lead to the known indentation traces of adhering chips generated by transport rolls or during restacking operations. Cut-off chips can also reach a subsequent point of chip removal and be chipped for another time, which also produces traces on the surface of the workpiece. In addition to these adverse effects on the surface of the workpiece, higher wear rates of the cutting edge result due to multiple chipping, particularly during machining of wood or wooden materials.
From DE 31 20 343 A1 a circular sawing device is known in which in saw blade exhaust channels have interiors that are provided open to a saw blade perimeter and directed approximately radially to a central zone leading to a collection space which is provided at a rack and connected to an exhaust system.
From DE 195 09 933 CI a milling tool for machining wood, plastics or the like is known with at least two cutting edges staggered on a perimeter with a leading pressing element that rises above a circumferential surface of a tool shaft and a lagging cutting edge that rises above the pressing element, with a gap between the cutting edge and the pressing element. From this document the connection of this gap with a cavity in the interior of the tool shaft is known, whereby the cavity has openings for chip disposal. The narrow gap combined with the pressing element is intended to minimize pre-chopping during wood machining. In this solution the setting of the gap between the cutting edge and the pressing element defines the cutting conditions. Additionally it is proposed to support chip disposal by an air current which is led longitudinally through the tool shaft.
From EP 0 367 255 A2 a wood machining machine for the production of flat chips is known that uses a powered, horizontally arranged cutting rotor with cutting knives, in which, in order to remove the chips in approximately axial direction, a stationary guide plate protrudes into an inner machining space, whereby the guide plate has a blade-like curvature, is positioned in a lower zone of the rotor and extends approximately over the full radial height of the inner machining space.
From DE 301 957 C a bell-shaped milling cutter for wood which is equipped with protective devices between the knife edges is known. A protective ring rests on a rim of the knives and protective elements to prevent springing. In an advantageous embodiment, the knife parts can be rotationally adjusted in relation to the protective ring by means of set screws, set wedges or the like. The chip slots in front of the cutting edges are equivalent in their geometry and function to the chip collection spaces of conventional tools and thus do not serve to remove the chips into the tool inner space.
It is the objective of this invention to provide, for milling tools with chip space or gap, a device for disposal of chips that requires little energetic and technical effort, prevents adverse effects on a generated workpiece surface and reduces wear of cutting edges.
According to the invention, the problem is solved by designing a chip space or gap as an opening for chip disposal with the opening running approximately perpendicular to a plane formed by a cutting edge and cutting direction, and having a cross-section bigger than a projected area of a chip cut off during the cutting action of the cutting edge.
In contrast to DE 195 09 933 C1, in this invention the opening is significantly bigger than a gap of DE 195 09 933 CI where it is regarded as technologically necessary to provide a very narrow gap (the principle of a plane""s mouth) combined with a pressing element for the improvement of the surface quality (minimization of pre-chopping).
Also in DE 31 20 343 A1, an only very small chip opening can be used due to the design so that the chips have to be forced together or fragmentized, respectively, so that they can pass then into the tool, or to the collection space, respectively, supported by an exhaust system.
The big cross-section of the opening for chip disposal of the present invention makes it possible that through it solid wood chips of a big cross-sectional area can unimpededly get into the tool, even if they are curled. The outwardly flowing air (centrifugal pump effect) only marginally impedes the chips in moving inwardly. Therefore the opening does not clog as quickly as a small gap.
In DE 195 09 933 C1 and DE 31 20 343 A1, a plan angle K of 90xc2x0 is used for technical reasons. Due to the design the chips move radially into the tool. In order to make the chips leave the tool, the direction of motion of the chips has to be changed with help of auxiliary energy (suction or compressed air, respectively).
In the first embodiment of the present invention the chips, axially accelerated during the cut-off process, move due to their high level of kinetic energy automatically along the cutting edge and the clapper over the opening for chip disposal in direction of the ejection opening, or the front face, respectively, without any energy separately supplied. Cutting is carried out using geometrically defined, straight or profiled cutting edges.
Equivalent to the front side ejection opening at the tool cavity, it is also possible to have the gap run through to the front face. Therefore no big tool cavity is necessary, which is advantageous, particularly, for tools of small diameters and/or high strength requirements.
It is advantageous to arrange the cutting edge with a plan angle K of between 60xc2x0 and 20xc2x0. In an advantageous embodiment, the front side ejection opening can also be designed conical.
The opening for chip disposal can be designed as an opening with a constant cross-section or with a cross-section widening in the direction of the front face. The cross-sections are designed as slots, or holes, respectively, requiring little technological effort.
The ejection opening and the tool perimeter are advantageously bevelled in accordance with the plan angle. Walls of the hollow tool body are set as thin as possible. This minimizes a path length of the chips into, or through the tool, respectively.
In order to prevent widening of the body, or cutting edge carrier, respectively, equipped with openings, at higher rotational speeds, it is advantageous to provide a clamping ring for improving the tool""s strength at the open side.
The front face of the milling tool is advantageously designed (as a tubular connection) to adapt a chip disposal device. The chip disposal device can be dimensioned to demand little power only for the transport of the cut-off wood chips from the tool to the chip bin.
Clamping of the cutting edges is designed to enable an unimpeded chip transport into the tool, or gap, respectively. Therefore, the cutting edge is attached to the tool body either permanently by brazing, bonding or the like, or replaceably with a clapper.
In a second embodiment of the present invention, in case of a plan angle K greater than 60xc2x0/70xc2x0, in an existing tool cavity in an interior of the milling tool a stationary thin-walled cylindrical to conical built-in component matched to a shape of the tool""s inner space is provided whose outer diameter is slightly smaller than that of the tool cavity, with at least one chip window in a region of the opening for chip disposal (region of action), which is dimensioned such that the chips can unimpededly enter into the remaining tool cavity.
In this embodiment the milling tool includes a rotating thin-walled tool body with at least two cutting edges staggered at a periphery and a gap in front of the cutting edges. Cutting is carried out with geometrically defined straight, or profiled, respectively, cutting edges. The chips are accelerated when being cut off from the workpiece by the cutting edge, and move in a direction of the tool cavity through the chip collection opening. In such a rotating tool body, air flows out of the gap (similar to the principle of the radial-flow centrifugal pump) against the chip motion and thus prevents, above all, the big solid wood chips from being transported further. The centrifugal force pushes them outwardly, or against the inner wall of the tool, respectively.
Due to the stationary cylindrical to conical built-in component with a chip window, the air volume in the tool cavity is prevented from being carried off so that it escapes no longer through the chip collection openings driven by the centrifugal force, thereby no longer impeding the movement of the chips into the interior of the tool or even pressing them out.
Hence the chips fly freely through the chip window and hit an advantageously inclined guide plate, which leads them axially out of the tool.
There are several alternatives for the chips to leave the tool. One of these is a gap between tool and motor/bearing plate. In this case, the cylindrical to conical built-in component is on feet or has an outlet opening in direction of the flight of the chips in the lower region of the built-in component. Another alternative is that the tool is designed open at a side opposite to the motor. In this case, the built-in component has to be fixed to the motor or frame through braces.
A supporting, axially operating exhaust system can be attached to the tool directly at the ejection opening. It is advantageous that this exhaust system can be operated with a small power just sufficient to transport the chips from the tool to the chip bin.
In order to prevent widening of the slotted bodies at higher rotational speeds, clamping rings can be provided at the open side of the tool.
The advantage of the present invention is that the chips move into the tool without any auxiliary energy needed and are transported off automatically.